1. Field of the Invention
The present invention relates to an electrophotographic photoreceptor (hereunder sometimes called simply a “photoreceptor”), and relates specifically to an electrophotographic photoreceptor provided with a photosensitive layer containing an organic photoconductive material on a conductive substrate, for use in electrophotographic printers, copiers, fax machines and the like.
2. Description of the Related Art
Conventionally, the principal type of electrophotographic photoreceptor has been the inorganic photoreceptor, which is provided with a photosensitive layer of an inorganic photoconductive substance such as selenium or selenium alloy or a photosensitive layer of a material containing an inorganic photoconductive substance such as zinc oxide or cadmium sulfide dispersed in a resin binder. Because of advantages such as flexibility, thermal stability, and film formation, however, organic photoreceptors have been developed in recent years provided with photosensitive layers of organic materials including organic photoconductive materials. Examples include photoreceptors having photosensitive layers composed of poly-N-vinylcarbazole and 2,4,7-trinitrofluorene-9-one, photoreceptors composed primarily of organic pigments, and photoreceptors having photosensitive layers composed primarily of eutectic complexes of dyes and resins.
A photoreceptor must have the function of holding a surface charge in the dark, the function of receiving light and generating charge carriers, and the function of receiving light and transporting charge carriers. These photoreceptors include monolayer photoreceptors, which combine all these functions in a single layer, and functionally separated stacked photoreceptors, which are obtained by stacking functionally discrete layers: primarily, a layer that contributes to generating charge carriers during photoreception, and a layer that contributes to holding a surface charge in the dark and transporting charge carriers during photoreception.
Of these, functionally separated stacked photoreceptors have recently come to predominate. In particular, there have been many proposals for negatively-charged photoreceptors in which the photosensitive layer includes a charge generation layer using an organic pigment as the charge generation material, which is either vapor deposited or dispersed in a resin binder together with a solvent to obtain a coating solution which is then coated to form the charge generation layer, laminated with a charge transport layer using an organic low-molecular-weight compound as the charge transport material, which is dispersed in a resin binder together with a solvent to obtain a coating liquid which is then coated to form the charge transport layer.
For example, phthalocyanine pigments and azo pigments, anthanthrone pigments, perylene pigments, perinone pigments, squarilium pigments, thiapyrylium pigments, quinacridone pigments and other organic pigments are known as charge generation materials. Moreover, pyrazoline compounds and pyrazolone compounds, hydrazone compounds, oxadiazole compounds, arylamine compounds, benzidine compounds, styryl compounds, butadiene compounds, terephthalic acid compounds and other organic low-molecular-weight compounds are known as charge transport materials.
For example, in the technique disclosed in Japanese Patent Application Publication No. H9-90654 an azo compound having a specific structure is included together with a triarylamine compound and/or distyryl compound in the photosensitive layer in order to provide an electrophotographic photoreceptor having high sensitivity, durability and repeat stability. Moreover, Japanese Patent Application Publication No. H3-196049 discloses an electrophotographic photoreceptor using a stilbene compound with a specific structure and a triphenylamine compound with a specific structure as charge transport materials. Furthermore, Japanese Patent Application Publication No. 2001-51434 discloses an electrophotographic photoreceptor using a triphenylamine compound with a specific structure as a charge transport material, while Japanese Patent Application Publication No. H11-84696 discloses an electrophotographic photoreceptor containing a hydrazone compound with a specific structure, a butadiene compound with a specific structure and a styryl compound with a specific structure as charge transport materials.
However, although photoreceptors using triphenylamine compounds as charge transport materials have excellent wear resistance, gradation and solvent crack resistance, as well as the advantage of low cost in comparison with other charge transport materials, they have also been vulnerable to light-induced fatigue among other problems.
That is, when the drum cartridge is left in a detached state before being mounted on the electrophotographic device, light from fluorescent lamps and the like used in interior lighting may shine on areas of the photoreceptor surface through gaps in the light-receiving part of the cartridge and the like. This causes light-induced fatigue of the areas exposed to light, which may result in problems of abnormal printing concentration in these areas when the cartridge is mounted on an electrophotographic device and used in printing.
It is therefore an object of the present invention to resolve the aforementioned problems and provide a good electrophotographic photoreceptor whereby costs can be controlled while reducing light-induced fatigue.